Cell Structure- topic 4

Question 1

what does a light microscope use to be able to see an image?

Answer 1

-lens is used to focus an beam of light to see an image

Question 2

what is the resolution of a light microscope?

Answer 2

-resolution is limited to half the wavelength of light involved= 0.2 micrometers apart

Question 3

what are the three parts of an animal cell visible in a light microscope?

Answer 3

-cell surface membrane
-cytoplasm
-nucleus

Question 4

what are the 7 parts of a plant cell visible in a light microscope?

Answer 4

-cell surface membrane
-cytoplasm
-tonoplast
-nucleus
-vacuole
-cell wall
-chloroplast

Question 5

how many micrometers are in a millimeter?

Answer 5

-1000 micrometers in a millimeter and there are 1000 nanometers in every micrometer
-millimeter=10 power of -3
-micrometer=10 power of -6
-nanometer=10 power of -9

Question 6

what does resolution mean?

Answer 6

-the ability to see two adjacent but separate points as distinct entities following magnification

Question 7

what is the difference in resolution in an electron microscope and a light microscope?

Answer 7

-electron microscope can resolve to 0.1 nanometers compared to light microscope can only achieve 0.2 micrometers
-this means that the electron microscope can achieve a greater magnification

Question 8

why is the electron microscope magnification better ?

Answer 8

-electrons have a shorter wavelength then light and so it has a greater magnification and resolution

Question 9

what are electron microscopes used for and why?

Answer 9

-shows cell ultrastructure which is much more complex and cannot be shown on a light microscope

Question 10

what is the advantages of a light and electron microscope?

Answer 10

-living specimens and biological processes can be viewed under a light microscope whereas matter has the be dead when using a electron microscope (this is because there must be a vacuum inside the electron microscope)
-electron microscope requires a lot more work as it must be cut very thin and stained to provide a contrast between the structures seen
-EM is more expensive

Question 11

what are the two types of electron microscopes?

Answer 11

-transmission electron microscopes
-scanning electron microscopes

Question 12

what is a transmission microscope involve, why is it used ?

Answer 12

-involves electrons passing through a very thin dead specimen
-it produces an image with a very high resolution and consequently can be used for very high magnifications

Question 13

why is a scanning electron microscope and what does it involve?

Answer 13

-involves electrons reflecting off the surface of the image as opposed to going through it
-resolution and magnification are not as high but it useful for giving a 3d image of surface features

Question 14

what is the difference between a eukaryotic cells and prokaryotic ? what are 3 types of eukaryotic cells?

Answer 14

-eukaryotic cell has a nucleus and membrane bound organelles and prokaryotic doesn’t
-animals, plants and fungi
-prokaryotic cells are bacterial cells

Question 15

what is the job of the nucleus and what does it contain?

Answer 15

-largest organelle
-contains DNA in the form of chromosomes which are wrapped around proteins called histones
-control center of the cell as the DNA in the chromosomes codes for the synthesis of proteins in the cytoplasm

Question 16

what is the job of histones?

Answer 16

-helps support and protect DNA

Question 17

what is chromatin? what are the 2 different types of chromatin?

Answer 17

-when cells are not dividing the chromosomes are not visible but are in the form of chromatin
-in parts of the nucleus chromatin can be more dense appearing dark called heterochromatin, in some it can be less densely packed and can appear lighter called euchromatin

Question 18

what are nucleoli? what is its job and what does it look like under an EM?

Answer 18

-the nucleus often contains more than one nucleoli
-nucleolus can appear even darker and dense than the chromatin
-it contains DNA that codes for the ribosomal RNA and so makes ribosomes which are transported out of the nucleolus through the nucleus and into the cytoplasm

Question 19

why is it good for chromosomes to be isolated in the nucleus?

Answer 19

-means the DNA is protected from any potential damage from the cytoplasm

Question 20

what is the job of the nuclear pores and the nuclear envelope?

Answer 20

-the DNA code for protein synthesis needs to be taken from the nucleus to the cytoplasm where protein synthesis takes place and also other molecules need to enter and leave the nucleus and so nuclear pore lets this happen
-nuclear membrane is a double membrane with a very narrow space between each membrane, the outer membrane is encrusted with ribosomes and is the site of origin for the RER
-messenger RNA that carries the genetic code from the DNA passes through the nuclear pores into the cytoplasm

Question 21

what is the structure and job of the rough endoplasmic reticulum? what structures of protein are synthesised on the RER?

Answer 21

-has ribosomes attached
-the RER provides the scaffolding for the ribosomes to make protein
-ER is joined to the nuclear envelope which helps to transport the mRNA which carries the DNA code, from the nucleus to the ribosomes
-primary structure of protein is synthesized on the RER, the secondary and tertiary structures are developed within the cisternae

Question 22

what is the structure and job of the SER?

Answer 22

-has a role in the synthesis of lipids, the detoxification of drugs and poisons and helps in the carbohydrate metabolism

Question 23

what is the structure and job of ribosomes?

Answer 23

-small organelles and are visible as small black dots in EM micrographs
-can be free in the cytoplasm or attached to the outer surface of the RER
-made of protein and ribosomal RNA and they frequently occur in groups creating hot spots of protein synthesis

Question 24

what is the structure and job of the Golgi apparatus?

Answer 24

-is a series of flattened curved sacs called cisternae, they also have a number of small vesicles both entering and leaving the cells
-main job is to label, package or export proteins

Question 25

what do the vesicles leaving the Golgi apparatus contain?

Answer 25

-contain newly synthesized protein pinch off from the RER and come together with the convex edge of the apparatus (the side closest to the nucleus)

Question 26

within the Golgi apparatus what ways can proteins be modified?

Answer 26

-can have carbohydrates added to form glycoproteins
-lipid can be added to form lipoproteins
-can have a prosthetic group or cofactors added
-different proteins/ polypeptides can be joined together to form quaternary structures

Question 27

what happens once proteins are modified in the Golgi apparatus?

Answer 27

-vesicles containing the finished proteins are pinched off from the concave face (usually the furthest away from the nucleus)
-these vesicles transport the protein either within the cells or fuse with the cell surface membrane to release their contents outside the cell

Question 28

what is the structure and job of the lysosomes?

Answer 28

-tiny vesicles of which the outer membrane is usually a more defined black membrane that is thick shown on an electron microscope image
-they are formed by the Golgi apparatus and contain hydrolytic enzymes for internal use
-they fuse with other vesicles that contain something that has to be destroyed or digested e.g. worn out cell organelles
-have a role in phagocytosis where they engulf and digest bacteria
-the thick membrane ensures that the lysosomes are not accidentally released inside the cell
-they also contain digestive enzymes

Question 29

do plants contain lysosomes and why?

Answer 29

-no because the functions of the lysosomes take place in the vacuole

Question 30

what is the structure and job of the mitochondria?

Answer 30

-present in all animal cells and are bean shaped
-enclosed with a double membrane separated by an inter membrane space, inner membrane is folded to form cristae that extend into the matrix of the mitochondria
-the infoldings increases the surface area which increases the number of enzyme that can be embedded within the membrane
-the mitochondria is the powerhouse of the cell and is the site of ATP synthesis during aerobic respiration
-lots of mitochondria are found in muscle cells and they also have more infolds (cristae) are more numerous

Question 31

what is the structure and job of the microtubules in animal cells?

Answer 31

-they are hollow cylinders formed from the protein tubulins and the form the cytoskeleton which helps to maintain cells shape and keeps organelles in place
-they also provide a network aiding the movement of structures within the cell

Question 32

what is the job of spindle fibres?

Answer 32

-important in the movement of chromosomes during mitosis and meiosis and are formed by microtubules

Question 33

what is the job of centrioles?

Answer 33

-involved in the assembly of spindle fibers during cell division are formed of microtubules and they are also important constitutes of the cilia and flagella

Question 34

what do the terms cytoplasm, protoplasm and cytosol mean?

Answer 34

-cytoplasm is the term used to describe the part of the cell between the membrane and the nucleus which includes all the organelles
-protoplasm is the term used to describe all the cell within the cell surface membrane
-cytosol is the term used to describe the fluid part of the cytoplasm only

Question 35

what are some features that are present in plant cells but are not in an animal cell?

Answer 35

-plant cell wall
-middle lamella
-plasmodesmata
-chloroplasts
-large vacuole
-tonoplast (membrane surrounding the vacuole)

Question 36

what is the structure and job of the plant cell wall?

Answer 36

-made of cellulose which is laid down as microfibrils
-provides support directly but also helps with turgor
-they restrict the outward expansion of cell contents as the cell takes in water and helps prevent the cell from bursting
-cell wall is fully permeable unlike the cell membrane which is semi permeable, cell wall plays no part in determining which substances can enter and leave cells

Question 37

what is the difference in the primary and secondary cell wall in plant cell?

Answer 37

-primary cell wall is made up of microfibrils that are in different and random directions, the loose arrangement of microfibrils allows the cell wall to expand as the cell grows
-when the cell reaches full size additional layers of cellulose is deposited to form the secondary cell wall
-the microfibrils are orientated in the same direction however additional layers are orientated in different directions which creates a lattice pattern which helps provide strength and support

Question 38

what do the terms flaccid and turgor mean?

Answer 38

-flaccid means that there is no water in the cell meaning no support
-turgor means that there is water in the cell and so the cell has support

Question 39

what is the structure and job of the middle llamella? how is it formed?

Answer 39

-adjacent cell walls are linked by the middle lamella
-it is formed by calcium pectate which forms a gel that acts as an adhesive that holds neighboring cells together

Question 40

what is the structure and job of the plasmodesmata?

Answer 40

-strands of cytoplasm that extend between neighboring plant cells
-they provide gaps in the cell walls which allow molecules to pass through, the plasmodesmata allows the cytoplasm to be joined continuously between the plant cells which allows them to be physically and metabolically joined

Question 41

what is the structure and job of the chloroplasts?

Answer 41

-bound by a double membrane which encloses stroma (fluid inside the chloroplasts)
-within the stroma is a system of membranes called thylakoids
-at parts of the thylakoids the membranes can be in stacks called grana, the less concentrated parts of the grana is called inter grana
-thylakoids contain the chlorophyll which is the site if photosynthesis
-chloroplasts also contain one or more starch grains which are produced by photosynthesis

Question 42

what is the structure and job of the vacuole in a plant cell?

Answer 42

-plant cells have a large vacuole within the cytoplasm
-it is important in the storage of ions and water and helps with the turgor of the cell

Question 43

do fungal cells have cell wall and if so what are they made of? what are organelles that fungal cells have?

Answer 43

-they do have cell walls but they are made of chitin instead of cellulose
-they have SER, RER, multi nuclei (they are multinucleate), vacuole, mitochondria, glycogen granules, lysosomes, ribosomes

Question 44

what are the similarities and differences between eukaryotic and prokaryotic cells?

Answer 44

-prokaryotic cells do not have a nucleus instead chromosomes are free in the cytoplasm
-DNA is circular in prokaryotes and is linear in eukaryotes
-prokaryotes do not have membrane bound organelles
-prokaryotes have a cell wall made of glycoproteins
-prokaryotes do not have microtubules but they do have plasmids

Question 45

what is the two components of the cell surface membrane? what is its function?

Answer 45

-a phospholipid bilayer and proteins
-the phospholipid bilayer forms the skeleton of the membrane which is due to the properties of the phospholipid molecules
-membrane is semi permeable which allows certain substances in and out of the cell

Question 46

what is the properties of phospholipid molecules?

Answer 46

-has a hydrophilic head that can mix with water but not lipids
-has a hydrophobic tail that can mix with lipids but not water

Question 47

what is the structure of the phospholipids and proteins in the bilayer?

Answer 47

-has two layers
-the hydrophobic tails turn away from the solution and align with other hydrophobic tails, whereas the hydrophilic heads readily mix with the surrounding tissue fluid and cytoplasm
-protein molecules are scattered throughout the membrane which they can be embedded into the layers known as intrinsic or can be attached peripherally to the bilayer known as extrinsic
-some proteins can extend throughout the bilayer known as transmembrane proteins

Question 48

what else to animal cells have in their cell membranes and what is its function?

Answer 48

-cholesterol molecules can also be present which lie between the phospholipid tails
-cholesterol increases membrane stability by restricting the sideways movement of phospholipid molecules at high temperatures. At low temps it helps maintain membrane fluidity and stops adjacent molecules sticking together
-makes membrane less fluid in high temps and makes membrane more fluid in low temps

Question 49

why is the cell surface membrane sometimes called a fluid mosaic model?

Answer 49

-the phospholipid molecules can flow sideways, although always keeping the bilayer arrangement, with the protein molecules floating between the phospholipid molecules

Question 50

what does the term glycocalyx mean in terms of the cell surface membrane? what are the different types of products made and what are their jobs?

Answer 50

-extending from the outer phospholipid layer of the membrane is the glycocalyx
-carbohydrates can bind to protein called glycoproteins or bind to the phospholipids called glycolipids (these are important in cell to cell recognition so similar cells can come together to form tissues)
-some glycoproteins can act as antigens which allows the body to recognize cells as normal cells and get rid of foreign bodies
-some glycoproteins can also act as receptor sites that allow specific molecules to fit, receptor sites also are important in hormone action and in the passage of neurotransmitters between neurons
-glycoproteins and glycolipids also form hydrogen bonds with water molecules outside the membrane which helps stabilize the membrane
-

Question 51

what are the two types of intrinsic proteins and what are their jobs?

Answer 51

-channel proteins span the membrane and create a hydrophilic channel that allows polar molecules (water based molecules) to bypass the hydrophobic center of the bilayer, they can either be permanently open or gated
-carrier proteins carry specific ions and molecules across the membrane, this may be because the molecules have charged groups e.g. glucose, or because the molecules or ions move against the concentration gradient. The carrier proteins can change shape to carry one substance from one side of the membrane to the other